The most customary way of obtaining such a frothy emulsion is to pour the desired amount of milk into a container, to immerse the steam outlet pipe in said container, shaking it up and down to get in the air necessary to form the froth. The quality of the froth obtained depends on the skill of the user who, when not a professional, may also be subject to splashing. For hygiene reasons, it will be appreciated that the pipe and the container containing the milk need to be cleaned after each use. As far as the economical aspect is concerned, the user needs to be capable of withdrawing just the right amount of milk from a standard packaging so as to avoid any wastage.
In order to avoid some of the abovementioned disadvantages and, in particular, in order to obtain a more uniform and homogeneous quality of froth, various types of venturi-effect devices have been proposed in order to act somewhat as an interface between the steam outlet of an expresso coffee machine and a container containing milk.
The simplest type of venturi-effect device, described for example in U.S. Pat. No. 4,800,805, consists in an air carrying tube secured to the steam outlet pipe and having its opening positioned below said outlet, the entity having to be immersed in a container containing the desired amount of milk. The improvement described in U.S. Pat. No. 5,335,588 consists in securing the air line to a sleeve which can itself be fitted to the steam outlet pipe, the entity still having to be immersed in a container containing the milk.
Patent EP 0 243 326 describes, for example, a venturi-effect accessory that can be fitted to an expresso coffee machine, comprising a great many parts making it possible, in an aspiration chamber, to have an arrival of pressurized steam which, through a venturi effect, entrains air along a first duct and entrains along a second duct milk arriving from a reservoir incorporated into the machine or aspirated from a standard packaging by means of an immersed connecting dip tube, this mixture then being injected into an emulsifying chamber before leaving in the form of a frothy emulsion.
An improvement proposed in U.S. Pat. No. 5,265,519 corresponds to a simpler design, with fewer parts to be assembled in order to form the venturi-effect device, and comprises an anti-splash cap at the frothy emulsion ejection orifice. When the packaging, the capacity of which is generally one liter, is used in industrial catering, the food liquid is used up quickly enough that there is no need to take special precautions regarding its shelf life, for example keeping it cold. For hygiene reasons, it is nonetheless still necessary to clean the dip tube, and periodically, the venturi-effect device. This device also has the disadvantage of not allowing the food liquid contained in the packaging to be used up completely.
Patents EP 0 803 219 and EP 0 803 220 B1 also describe a device for preparing an emulsified milk or cappuccino by pumping by means of two tubes immersed in a container of the “cardboard carton” type and connected to a venturi-effect device. This device also requires frequent cleaning and requires the milk package to be kept at a refrigerated temperature by a cooling system associated with the device.
Patent application WO 02/087400 relates to the preparation of a frothed drink using a capsule containing an ingredient that can be frothed. The principle is to inject a liquid into the capsule in order to perform the mixing, to release the mixture through the capsule into a receptacle and then inject further liquid in the form of a jet so as to produce a frothed liquid in the receptacle.
Patent application WO 01/58786 relates to a cartridge for preparing a frothy drink which comprises, near or directly at the drink outlet, restriction means making it possible to produce a jet of drink, at least one air inlet and means for generating a pressure reduction. The mixing of the drink is performed in a mixing compartment situated upstream of the restriction means and sufficient excess pressure is required in the compartment to force the drink through the restriction means. Such a cartridge is suitable for extracting a drink from a substance of the roasted-ground type.
When the packaging is used in a communal or family setting, and with the knowledge that, for example, a liter of milk will make 30 to 50 helpings of cappuccino, it is necessary either to put the packaging back in a refrigerator after every use, or to place it in a mini-refrigerator with which the coffee machine is equipped, it then being possible for the dip tube to remain constantly connected. This solution has the advantage of reducing the number of times the dip tube has to be cleaned, but has the disadvantage of making the equipment necessary for producing the frothy emulsion more expensive and therefore of increasing the cost price of the final consumer product.